marsh gas: see methane methane (mĕth`ān), CH₄, colorless, odorless, gaseous saturated hydrocarbon; the simplest alkane .
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methane

or marsh gas

Organic compound, chemical formula CH₄, colourless, odourless gas that occurs in natural gas (called firedamp in coal mines) and from bacterial decomposition of vegetation in the absence of oxygen (including in the rumens of cattle and other ruminants and in the gut of termites). The simplest member of the paraffin hydrocarbons, methane burns readily, forming carbon dioxide and water if supplied with enough oxygen for complete combustion or carbon monoxide if the oxygen is insufficient. Mixtures of 5–14% methane in air are explosive and have caused many mine disasters. The chief source of methane is natural gas, but it can also be produced from coal. Abundant, cheap, and clean, methane is used widely as a fuel in homes, commercial establishments, and factories; as a safety measure, it is mixed with trace amounts of an odorant to allow its detection. It is also a raw material for many industrial materials, including fertilizers, explosives, chloroform, carbon tetrachloride, and carbon black, and is the principal source of methanol.

marsh gas

a hydrocarbon gas largely composed of methane formed when organic material decays in the absence of air

marsh gas [′märsh ‚gas]

(geochemistry)

Combustible gas, consisting chiefly of methane, produced as a result of decay of vegetation in stagnant water.